Expanded metal has many applications, as for example in air filters, ventilation systems, strainers, etc. Typically, expanded metal is formed by feeding metal sheet or plate (herein after referred to as “base plate”) 12 through feeders 14 which is then fed through an expander 16, where it is expanded to form expanded metal 15. The expanded metal is then fed through flattening rolls 18 and into a take-up spool 20, as for example shown in FIG. 1. The feeders 14 are shown in FIG. 1, by way of example, as rolls. The feeder may be any device that feeds the base plate 12 from its spool 22 to the expander. The feeder may also be part of the expander. The expander includes a support base 24 over which is advanced to the base plate 12 (FIGS. 2A, 2B, 2C, and 2D). As the base plate is advanced, a desired strand thickness 26 beyond an edge 29 of the support base (FIG. 2B), a serrated cutting die 28 descends and simultaneously shears, slits and cold forms an entire row 30 of half-diamonds 32, as for example shown in FIG. 2C. The die then ascends and moves over a half-diamond to the right, as for example shown by arrow 3 (or the left in another embodiment) as the base plate is moved forward by another strand thickness beyond the edge of the support base. The die then descends and slits and cold forms another full row 34 of half-diamonds 36, completing a row of full raised diamonds 40 in two strokes, as for example shown in FIGS. 2C and 2D. As can be seen, each diamond is formed from four integral strands 37. The die then descends and returns to its initial position, as shown by arrow 4 in FIG. 2D, and begins to form another row of half-diamonds as the base plate is advanced to another strand width beyond the edge of the support, as for example shown in FIG. 2E. The formed raised expanded metal is then moved by the flattening rolls 18 where it is flattened and further cold worked so as to flatten the expanded material strands 37, especially in the areas where the vertices 44 of the diamonds are integrally connected forming what is commonly referred to as a “bond” 46, which typically has twice the width as the normal strands that exit the expander. The flattening rolls also pinch and pull on the expanded metal typically at a rate faster than the rate of the expanded metal exiting the expander. This causes the expanded metal to stretch by desired amount. In addition, the cutting die 28 also provides resistance against the pulling of the expanded metal by the fattening rolls.
An expanded metal has a “long way of diamond” dimension (LWD) 48, which is along the direction transverse to the direction that the base plate is fed through the expander and a “short way of diamond” dimension (SWD) 50 which is measured along the direction which the base plate is fed through the expander (FIG. 3). Conventional expanded metals have an LWD that is about twice the SWD.
Conventional expanded metals and process by which they are made are described in the “Standards for Expanded Metal Material” published by the National Association of Architectural Metal Manufacturers, NAAMM Standard, EMMA 557-99The contents of this publication are fully incorporated herein by reference.
When forming filters for residential, commercial use, expanded metal is attached to one side of the filter material and the filter material is then bent into an accordion fashion to faun a pleated filter. With conventional expanded metal, Applicants have discovered that after being pleated, the expanded metal has a tendency to attempt to spring back to its original shape. Thus, consistent pleats are not obtained, as some pleats after being formed spring back more than others. Another problem with filters incorporating conventional expanded metal is that the pleated filter has pleats which do not have consistent heights. As a result, the pleats have an increased chance to collapse during filtering due to the air pressure acting on the filter, resulting in premature failure of the filter. Furthermore, there are less contact points between the pleat peaks and bonds, thus, causing filter fluttering or possible pleat collapsing, which can reduce filter optimal performance. As such, expanded metals that would allow for more consistent pleating of filters and more consistent height pleats are desired.